306 



FORESTRY AND IRRIGATION 



June 



corrugated, so as not to leave a smooth 

 surface. The slope of the embankment 

 should be about 3 to i on the water side 

 and 2 to i on the lower side, and the 

 top width should be not less than 5 to 

 10 feet. 



An ample spillway should be provided 

 in some location where the waste waters 

 may be discharged without injury to the 

 dam, and should be of such a capacity as 

 to discharge the highest flood to which 

 the drainage basin is subject, without 

 danger of overflowing the dam. 



Provision for drawing off the water 

 may consist of a cast-iron pipe in the 

 bottom of the ravine under the dam, 

 ' with the earth carefully puddled and 

 packed around it on all sides to prevent 

 percolation along the pipe. It would 

 be still better to lay the pipe wholly or 

 partly in a bed of concrete, as this can. 

 be tightly bonded with the earth. The 

 pipe, of course, would be provided with 

 suitable valves for opening or closing 

 the outlet. 



In regard to the flow which the 



ditches should have, this depends upon 

 many factors. The most important of 

 these factors is the quantity of water 

 which it is intended to carry. The fol- 

 lowing is a table which may be of use. 

 The slope, as stated, is the least allow- 

 able for each case, and a somewhat 

 greater slope would be better, but it 

 should not be very much greater. 



The column marked ' ' bed-width ' 

 means the bottom of the ditch. It is 

 assumed that the side slopes will be i % 

 horizontal to i vertical ; the discharge 

 is given in cubic feet per second, and 

 one cubic foot per second is equal to 

 450 gallons per minute. 



Pumping Water for Irrigation* 



Mr. A. B. Fowler, of Guernsey, Wyo- 

 ming, writes that he has a pumping plant 

 belonging to Mr. E. F. Hurdle and him- 

 self, consisting of a second-hand 70- 

 horse power boiler and 5o-horse power 

 engine, costing $1,500 in place. The 

 running expenses amount to $5 per day 

 for labor and fuel. By means of it 7 

 cubic feet of water per second are raised 

 to a height of 20 feet. This amount of 

 water irrigates one acre per hour of 

 crops planted in rows, and one-half an 

 acre per hour when used in flooding. 

 The pump is estimated to furnish suffi- 

 cient water for 500 acres in diversified 



crops, but up to the present the engine 

 has not been operated for more than one- 

 third of the time in any season, as yet 

 only about 200 acres of land being under 

 cultivation. 



This device has been an unqualified 

 success, and would be in any other simi- 

 lar locality where an abundance of water 

 can be had. For such a plant to be 

 profitable it is necessary to have a good 

 market for the crops raised, or plenty 

 of live stock to feed. It is probable, 

 however, that water is obtained in this 

 way as cheaply as can be had through 

 ditches. 



Amount of Water Required to Irrigate an Acre. 



A cubic foot per second flowing 

 through an irrigation season of one hun- 

 dred days will deliver about 200 acre- 

 feet, or will cover 100 acres 2 feet in 

 depth. In most localities this is suffi- 

 cient water for the production of an 

 average crop. In California, where 

 water is scarce, less is used, and for 



orchards twice as large an area can be 

 irrigated. 



When irrigation is first practiced more 

 water is needed to thoroughly wet the 

 subsoil, but after a few years a less 

 quantity is required, and in some locali- 

 ties, as at Fresno, California, no water 

 is applied on the surface, the seepage 



